Controlling the Radicals: The Search for the Plant Enzyme Catalase

Mammals possess a specific immune system that acts as a defense against disease while plants react to pathogen attack by activiating novel defense mechanisms which are poorly understood compared to mammals. Plant defense mechanisms are activated not only at the site of infection, but also in neighboring cells and distant uninfected tissues. In recent years, intense study of plant defense has implicated the involvement of the active oxygen radical, hydrogen peroxide (H2O2), with key events in the initiation of plant defense. Much of the work in the field has been descriptive, identifying when and where H2O2 production occurs, but little is understood about the cellular mechanisms that govern the role of H2O2 in plant defense. Our lab has shown that H202 may be an intercellular signal capable of activating plant genes responsible for defense as well as localized cellular necrosis resulting in pathogen death.

We have now focused our attention on the plant enzyme catalase which converts the cytotoxic oxygen radical, H2O2, into water (H2O) and molecular oxygen (O2). Our working hypothesis is that in order for H2O2 to accumulate and prevent pathogen infection, p[lant catalases must be inhibited during pathogen attack. In order to test this hypothesis with current molecular tools, we have begun a set of experiments that will culminate in cloning of the gene that codes for the enzyme catalase from bean plants. Here we describe our efforts to clone the catalase gene from a library, restriction map the gene, and DNA sequence the putative catalase clone. If successful, the catalase clone can be used to test our inhibition hypothesis.